The present invention relates to a hydraulic/spring door operator with an overtravel restraint for preventing excess opening due to high wind force or the like.
Conventional door operators rely on hydraulic pressure and/or spring compression to provide controlled opening and closing forces, and typically employ a positive mechanical limit stop when the door reaches its extreme opening travel. Such mechanisms, the typical mounting and linkage arrangement of which is shown in FIG. 1, are characterized by a sharp reduction in the restraining force at opening angles above approximately 130.degree., as shown by curve (a) in FIG. 2. This is due, inter alia, to the decreasing pinion axis rotation at high opening angles, as shown in FIG. 3, the decrease in the spring force as it approaches its maximum compression, as shown by curve (b) in FIG. 2, and the changing mechanical advantage of the two pivotally connected level arms coupled between the door frame and the pinion axis of the operator mechanism. As a result, if a severe opening force is applied, as when a high wind catches the door as it is being opened, the door handle is frequently jerked out of the operators hand and the door is rapidly thrust against the limit stop in the mechanism to cause the rupture or damage thereof.